Short circuiting plug for coaxial line



Sept. 18, 1956 O. T. LAUBE SHORT CIRCUITING PLUG FOR COAXIAI.. LINEFiled Nov. 28, 1952 United States Patent O SHORT CIRCUITI-NG PLUG FORCOAXIAL LINE Otto Theodore Laube, East Orange, N. J., assigner toAmerican Telephone and Telegraph Company, a corporation of New YorkApplication November 28, 1952, Serial No. 323,030

7 Claims. (Cl. 333-97) This invention relates to a short-circuiting plugand more particularly to an adjusting short-circuiting plug for coaxialtransmission line sections.

In transmission systems it is sometimes desirable to use a section ofcoaxial line of a length resonant at some particular frequency, with theend of the line terminated in a short circuit. For example, an unwantedfrequency may be suppressed by connecting a length of line terminated ina short circuit to the feed line f a radio receiver or transmitter. Theshort circuit is positioned so that the line section resonates at theunwanted frequency. Such a stub, usually with a companion compensatingstub of similar construction, constitutes a widely used form of radiofrequency filter. Similar coaxial line sections are used for impedancematching.

Proper functioning of short-circuited line sections in these and otherapplications depends in considerable measure on the accuracy achieved inadjusting the length of line section since this determines the frequencyat which the line will resonate. In addition, the means used to providethe short circuit between the inner and outer conductors must be such asto assure good contact.

Heretofore, the construction of such short-circuited transmission linesections has involved cut and try processes wherein the line itself wasprogressively shortened by sawing or other means. This method islaborious and has the further disadvantage of precluding backing ofi ifthe adjustment has gone even slightly below the optimum length. Accuratetuning is achieved only by application of painstaking and time-consumingmethods.

Other short-circuiting means utilizing resilient lingers with contactpoints aiiixed thereto provide a discontinuous short-eircuiting path andthereby introduce stray loss into the circuit.

General objects of this invention are to overcome the above-mentioneddifficulties and provide a structurally simple and eiiicientconstruction for short-circuiting coaxial line sections.

A further object is to expedite and facilitate accurate tuning ofcoaxial transmission lines.

These and other objects of this invention are realized in one specificembodiment in a plug comprising a flat diaphragm or washer fittedbetween the corresponding ends of two coaxial cylindrical members. Meansare provided for moving the inner cylindrical member and Washer relativeto the outer member. The ends of the cylindrical members housing thewasher may be made resilient and by suitably shaping the engagedsurfaces of the cylindrical members and the washer the resilient ends ofthe cylindrical members are caused to grip their adjacent coaxialconductors when the inner member and washer are moved axially. The planesurface of the washer thereby becomes the short-circuiting path betweenthe inner and outer coaxial conductors. Preferably, a tool is providedfor positioning and clamping the plug in place within the coaxial linesection.

The invention in one aspect therefore comprises means for simultaneouslygripping the inner and outer conductors at a desired location within acoaxial line section.

Another feature involves a particular shape of the inner and outerperipheries of the washer and the cooperating surfaces on the inner andouter cylindrical members whereby the plug is securely clamped to thecoaxial conductors. A resultant advantage thereof is the provision of ashort-circuit path composed of the face of the washer in substantiallyline contact with the inner and outer conducting surfaces.

The invention and the above-noted and other features thereof will beclearly understood from the following detailed description when read inconnection with the accompanying drawing in which:

Fig. l is a side elevation View, partly in section, and illustrates theplug in position within a section of coaxial transmission line;

Fig. 2 is an exploded view in perspective of a plug assembly constructedin accordance with this invention;

Fig. 3 is a side elevation View, partly in section, of a tool forpositioning the plug illustrated in Figs. l and 2, within a section ofcoaxial transmission line.

Referring now to the drawing, the plug therein illustrated may beconstructed of any suitable conducting material, for example brass, andcomprises an outer hollow cylinder 11, a washer 12, a tube or innercylinder 13, an end plate 14, and a nut 15.

As shown in Fig. l, the tube 13 is positioned coaxially Within the outercylinder 11. The inner or clamping ends of the tube and cylinder arecoincident in crosssection and are rendered iiexible by the provision oflongitudinal slots 16. The outer cylinder 11 is closed at itsnon-liexible end by the end plate 14. The tube 13 is longer than theouter cylinder 11 and protrudes through the central aperture of the endplate. The nonflexible end of the tube is provided with a threadedportion 17 on which the nut 15 is threaded. The nut has recesses 23 intowhich the lugs of a wrench may be inserted for rotating the nut.

The washer 12 is iitted over the tube 13 and within the outer cylinder11 at their flexible ends. The chamfered inner periphery 18 and outerperiphery 19 of the washer form cam surfaces. The follower surfacesconsist of the conical or flared portion 20 of the tube and the insidetapered surface 21 of the outer cylinder The angles of these areexaggerated in the figure in order to present the manner of theircooperation clearly. The shoulder 22 on the iiexible end of the tube isa retainer for the washer.

The tool illustrated in Fig. 3 comprises an inner tubular member 24having an internally-threaded portion 25 adjacent one end adapted toengage the threaded portion 17 of the tube 13. The other end of theinner tool member 24 is provided with a knurled handle 26. Coaxial withand slidably fitted over the inner tool member is the outer tool memberor wrench 27. The outer tool member is likewise furnished with a knurledhandle 30 at one end. At the other end the member is provided with ashort length of increased diameter 2S terminating in lugs or iingers 29adapted to engage corresponding recesses 23 in the nut 15.

Tuning is accomplished by sliding the plug to the desired location inthe line. Thus, in a radio system for example, where the stub isconnected to the transmitter feed line, the plug is positioned byutilizing a radio receiver to determine when unwanted frequencies havebeen blocked out. Where the stub is in the feed line to the receiver,the plug may be located so as to suppress selected frequencies emittedby a signal generator. Where Vwith the inner conductor 32.

a companion stub is 'provided to compensate for the reactance of thetuning stub, the short-circuiting plug is positioned in the compensatingstub to produce the optimum power.

To short-circuit a section of coaxial line the tool is aiixed to theplugassembly byscrewing the threaded end 2S of the inner tool member 24on thethreaded end" end plate 14 and further rotation pullsV the tubeaxiallyV toward the open end of the line section. Axial motion of "thetube 13 draws the washer 12 in the same direction. The outer periphery19 of the washer cams the follower surface 21 of the outer cylinder 11outward into tight contact with the inner' surface of the outerconductor 31'.

Coincidently as the tube moves, the washer is restrained by the outercylinder and .moves a lesser axial distance than the tube. The innerperiphery 18 of the washer cams the follower surface 20 of the tubeinward contracting the flexible end of the tube into gripping contactThe tool may then be disengaged and withdrawn leaving the plug clampedin the line section.

To relocate or remove the plug the tool is reengaged and the nut 15backed-off. The tube may then move inward axially, the shoulder 22 onthe tube serving to force the washer 12 inthe same direction. Thismovement withdraws the cam surfaces 18 and 19 from the follower surfaces20 and 21 whereupon the flexible end of the tube expands and that of thecylinder contracts thereby unclamping the plug.

It is to be understood that the above-described arrangement isillustrative of the application of the principles of this invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

l. A device for short-circuiting a section of a coaxial transmissionline comprising a hollow cylinder for fitting within the outerVconductor and a tube forl fitting over the inner conductor, each havingequi-spaced longitudinal 'slots extending from one end, means for movingsaid tube axially relative to said cylinder, a washer f1tting within thecylinder and over the tube at their respective slottedportions,saidlwasher adapted to move axially with said tube, said washer, tube,and cylinder having adjacent contacting conical surfaces meeting at anacute angle, said surfaces cooperating to force the slotted portions ofsaid cylinder` and said tube into contact with said outer and innerconductors respectively, when said tube is moved axially.

2. Means for short-circuiting a section of a coaxial transmission linecomprisinga hollow cylinder adapted to lit within the outerlconductor ofthe line and atube adapted to fit over the inner conductor of the line,each having equi-spaced longitudinal slots extending from one end, awasher iitting within the cylinder and over the tube at their respectiveslotted portionsand adjacent the end of each, said washer, tube, andcylinder having adjacent contacting conical surfaces meeting at an acuteangle, said tube vhavinga threaded-portionv adjacent the end oppositethe slotted portion, a plate for iitting against of said washer and saidtube and cylinder cooperatingk to force 'said slotted portion of' saidYtubeand 'cylinder` into respective gripping contact with the inner andouter conductors of the line.

3. In combination, a short circuiting device in accordance with claim 2and a device for fixing said short circuiting device in a section ofcoaxial transmission line comprising two hollow coaxial sleeve members,the inner of said last-mentioned members being of greater length andhaving an internally threaded portion at one end for engaging'thethreaded portion of the tube member of said short circuiting device, theouter of said coaxial sleeve members having means at the end adjacentsaid threaded end of said inner member for engaging the nut member ofsaid short circuiting device, whereby rotation of said outer coaxialsleeve member with respect to said inner coaxial sleeve member causesrotation of said nut member relative to said short circuiting device.

4. Short circuiting means for a concentric conductor line, said meanscomprising a conductive cylinder tting within the outer conductor and aconductive tube embracing the inner conductor, said cylinder and tubeincluding flexible portions, and a short circuiting washer fittingWithin said cylinder and upon said tube at their respective flexibleportions, said washer having sloping external and internal surfacesmutually inclined to juxtaposed sloping surfaces on the cylinder and thetube respectively for camming thecylinder and tube into contact with thecorresponding concentric conductors upon axial movement of said tube,the lit between the cylinder, the tube,'and the Washer being such that aplane, uninterrupted short circuiting surface is presented to the line.

5. A device for short circuiting a section of a coaxial transmissionline comprising a hollow cylinder for slidably iitting within the outerconductor of said line anda tube for slidably tting over the innerconductor of said line, each having equispaced longitudinal slotsextending from end, means for moving said tube axially relative to saidcylinder, a circularplate washer fitting Within the cylinder and overthe tube at their respective slotted portions, said washer adapted tomove axially with said tube, said washer, tube, and cylinder havingadjacent mutuallyinclined, substantially line contacting surfaces, saidsurfaces cooperatingwhereby Ysaid, washer cams the slotted portions ofsaid cylinder and said tube into contact with said outer and innerconductors respectively, when said tube is moved axially with respect tosaid cylinder.

6. Means for terminating a section of coaxial transmission lineconsisting of an inner and an outer conductor, said means comprising acircular washer member having dimensions so as to substantially occupythe cross Vsection between said inner andouter conductors, said washerhaving inner and outer peripheries comprising inclined camming edges,means for securely positioning said washer member within said linebetween said inner and outer conductors, said means comprising a hollowcylindrical memberlarranged to iit slidably within said outer conductorand having a longitudinally slotted, flexible end portion and aninternal camming surface for engaging the outer periphery of saidwasher, and a tubular member arranged to lit slidably over said innerconductor and having-a longitudinally slotted, ilexible end portion,said end portion having a camming surface for engaging the innerperiphery of said washer'and a shoulder portion for retaining saidwasher, and means for moving said tubular member axially with respect tosaid hollow cylindrical member within said transmission line wherebysaid washer member is urged axially with said tubular member beingrestrained therefrom by engagement with said hollow cylindrical lmemberwhereby said flexible end portions of said hollow cylindrical member andsaid tubular member are urged respectively into clamping engagement withsaid outer and inner conductors.

7. Means for terminating a sectionof coaxial.V transmission line inaccordance with claim 6 in which said means for moving said tubularmember axially corn- 5 6 prises a rotatable member threadably engagingsaid tubu- 2,531,519 Kumpf Nov. 28, 1950 lar member and adapted totransmit thrust to said hollow 2,644,929 Kumpf July 7, 1953 Cylindricalmember. FOREIGN ':ATENTS References Cited in the le of this patent 5579,276 Great Britain July 30, 1946 UNITED STATES PATENTS 2,203,806 WolfJune 11, 1940

